The present invention relates to punching presses of the type such as disclosed in U.S. Pat. No. 3,107,567. More particularly, the present invention relates to apparatus for protecting the tools of hydraulically operated fine-punch presses for which the closing process is controlled through an end-switch controlled keying gap in the tool or table area and wherein the press table is moved through quick-closing pistons arranged in addition to the main or ram piston means.
It has been contemplated to protect against breaking of tools and fine-punch presses in such a way that a micro-switch is arranged at each of the ram and keying table and that, during movement together of the tool, the keying table is raised by a small amount. During this process, one of the switches is adjusted such that it is operated immediately before the raising of the keying table. If, during operation, the tool is not blown out clean or if the previously punched part has not been thrown out in an orderly fashion, then the second switch, arranged at the keying table, responds before the runner arranged in the ram area during the next stroke. An electronic-electrical control associated with the machine monitors the switching cycle and also controls the mechanical end switches and stops the machines in case of an interference such as mentioned above.
An important disadvantage of the above-described arrangement is that, through the arrangement of the keying unit at the mounting plate for the machine table, the required working or running clearance for same disadvantageously influences the tool guidance so that the quality of the stampings and edge life of the tools are decreased.
In order to avoid the above-noted disadvantages, the present invention contemplates an arrangement including so-called keying pistons connected in series with the quick-closing pistons and extending in the same direction of action. In a preferred embodiment of the present invention, it is further provided that the quick-closing pistons are arranged in the lower crosshead of the press and the keying pistons engage the ram through cantilever sections or the like.
With the arrangement of the present invention, the keying function is shifted (from the table plates as described in the above-noted arrangement) in a pair of quick-closing pistons arranged laterally of the press ram piston whereby the press table and mounting plate remain solidly connected with the major parts of the machine. That is, all machine elements required for the quality of the stampings are free of additional movements needed for protecting the tools against breakage. In other words, with the above-discussed previously contemplated arrangement the supporting press table was moved in order to accommodate the protection of the tools, while in the arrangement of the present invention, the keying pistons and keying gap are arranged at the moving press ram in conjunction with the quick-closing pistons, thereby obviating the necessitating of moving the opposing support table or the like.